Wave amplifier



R. K. POTTER WAVE AMPLIFIER July 5, 1938.

Filed Jan. 22, 1935 2 She ets-Sheet l INVENTOR RZITPOZZ er ATTORNEY R. K. POTTER WAVE AMPLIFIER July 5, 1938.

Filed Jan. 22, 1935 2 Sheets-Sheet 2 INVENTOR EEPOZZEI" ATTORNEY Patented July 5, 1938 PATENT OFFICE WAVE AMPLIFIER Ralph K. Potter, Madison, N. 1., assignor to American Telephone and Telegraph Company, a corporation of New York 20 Claims.

An object of my invention is to provide new and improved apparatus and method for the amplification of electromagnetic waves. Another object is to provide for the amplification of waves 5 of high frequency. In one aspect my invention is an amplifier of considerable length in the direction of transmission, this length being in some cases several wave lengths. The fact that the electrodes of. the amplifier extend along its length for one or more wave lengths enables the amplifier to gather the incoming wave energy along its length and gradually build up amplified outgoing wave energy along its length. Such an amplifier as contemplated herein may be well adapted to be interposed in a high frequency concentric conductor system.

The foregoing objects and aspects of my invention will become more readily apparent on consideration of a limited number of specific examples of the invention which I have chosen for disclosure in the following specification. It will be understood that this specification relates principally to these particular embodiments of the invention, and that the scope of the invention will be indicated in the accompanying claims.

Referring to the drawings, Figure 1 is a diagrammatic longitudinal section of. a three-electrode vacuum tube interposed in a concentric conductor system and exemplifying my invention; Fig. 2 is a cross-section taken on the line 2 in Fig. 1; Figs. 3 and 4 are vector diagrams which will be referred to in discussing the principles involved in the practice of my invention; Figs. 5 and 6 are highly diagrammatic longitudinal :15 sections showing wave forms which will be referred to in explaining the principles involved in my invention; and Fig. 7 is a detail longitudinal section showing certain changes for an indirectly heated cathode instead of the directly heated M cathode of Fig. 1.

Referring to Fig. 1, the concentric conductor system comprising the axial conductor l2 and the outer conductor or shell H is adapted for transmitting high frequency currents from left to right. The outgoing members of this conductor system are indicated at l I and I! on the right.

A three-electrode vacuum tube has the outer metallic shell or anode l3 closed at the left by the glass seal l4 and at the right by the glass 50 seal I4 and the end wall I6. Coaxially disposed therein is a grid l5 stamped with comparatively long closely spaced longitudinal slots. On the left this grid I5 is turned out in a plane annular flange i6 opposite a similar flange I1 on 5.3 the end of the concentric conductor shell ll.

Application January 22, 1935, Serial No. 2,968

These two flanges I6 and I! may be regarded as the plates of a condenser so that by virtue of displacement currents between them there is electrical continuity between the shell II and the grid l5.

Lying close to the axis of the tube is a hairpin cathode-filament I8, its two ends being on the left and its return bend being at I2" on the right. At its right-hand end the grid I5 is extended beyond the glass seal I4 as an unperforated shell l5 and closed across by the end wall IS. A disk i9 is placed parallel with the end wall It, and from its edge the conical conductor 30 tapers down to the right and merges into the axial conductor l2 of. the concentric conductor system on the right. The cross walls I6 and H! are the plates of a condenser and afford virtual electrical continuity from the grid l5 to the axial conductor l2.

The circuit of the cathode battery 2| supplying heating current throughthe inductance 22 for the filament-cathode I8, is readily apparent. The axial conductor l2 incoming on the left is conductively connected to the axial filamentcathode l8 at 20. The anode circuit battery 24 is connected to the filament-cathode through the inductance 22 and to the anode at l3. Also,v there is a grid biasing battery 23 connected in the usual Way.

At the left end, the tube shell or anode l3 ends in the part 25. Just within this is a short cylindrical shell 26 spaced slightly from 25. This shell 26 is connected to the grid l5 by an annulus 21 of resistance material. The members 25 and 26 are the plates of a condenser. With the resistance disc 21 they afford a capacity-resistance connection across between the grid l5 and the anode shell 13 at the left.

On the right a short axial conductor rod l2' is electrically connected at I2" to the bent end of. the hair pin filament l8. Within the terminal part l5 of. the grid l5 and around this extension conductor IZ' is the short cylindrical shell 26' spaced slightly from I5 so that the two members l5 and 26' may be regarded as the plates of a condenser. The annulus 21' of resistance material connects the extension conductor l2 to the condenser plate 26. Thus the elements i5, 26, 21 and l2' constitute a capacity-resistance bridge across between the grid [5 and the filament-cathode H3 at their right-hand ends.

On the right the anode shell l3 has an outwardly directed plane annular flange 28: closely opposed to this is a similar annulus 29 with a connected conical tapering shell 3| extending wave as it is propagated along the length of the electrode of the tube. If the electrodes are more than one wave long, corresponding elements. of successive waves propagated along the electrodes are superposed upon each other to increase the amplification of the wave. The wave entering the tube at the left may be thought of as represented by radial lines of force with their inner ends on the axial conductor 12 and their outer ends on the inner face of the cylindrical shell ll, these lines of force being alternately directed outwardly and inwardly as one goes along the length of the conductor system atone instant, but all moving withthe speed of transmission from left to right. There is virtually acontinuous electrical connection from the shell ll through the condenser "-16 to the grid I! so that these waves of lines of force continue their progress within the vacuum tube, their inner ends traveling on the filament-cathode i|8 and their outer ends on the grid l5. If we consider a short length of the vacuum tube such as that between the lines 2 and 2 in Fig. 1, it may be looked upon as, in principle, a complete ordinary vacuum tube, provided the section of tube is so short as compared with a wave length that there is no variation in potential along the length of any electrode within the section. In the absence of any incoming waves there will be a steady stream of electrons from the filament-cathode l8 through the openings in the grid I5 to the plate l3. When waves come along to the segment 2-'-2', the density of this electron stream will be increased or diminished according to the direction of the lines of force of those waves. Thus the incoming waves will determine amplified outgoing waves' in the concentric conductor system whose axial conductor is the grid l5 and whose surrounding shell conductor is the anode 13. These outgoing waves will pass from the conductors I5 and I3 through the capacity connections l6'-|9 and 2829 to the sonically tapered pair of conductors 30 and 3|, and thence to the normal size axial conductor l2 and shell conductor 1 I of the outgoing concentric conductor system on the right.

Any elemental change in the anode current in the tube segment 22' will tend to create a wave disturbance going both right and left therefrom. At any particular point on the right, the wave elements arriving from the left will tend to add as vectors, as shown in Fig. 3. Qn the other hand, at any particular point on the left, the wave elements will tend to add as vectors, as indicated by the diagram in Fig. 4. This is in accordance with ordinary well-known wave transmission theory. Hence in great measure if not entirely, the incoming waves from the left will determine very little wave disturbance going to the left but will be amplified substantially going to the right. The capacity connection 25-26 and the resistance 21 interposed in series to each other as a bridge at the left between the conductors I5 and I3, will be designed to aflord a proper impedance termination, so that, in so far as there is set up a wave transmission to the left.

' ing connection.

For an applied wave of a given length the electrodes must be at least one wave length long in order that the vectors representing propagation of energy back towards the impedance 21 will add up algebraically to zero. Under these conditions there is no propagation of energy in this direction. The same will hold true when the electrode length is a multiple of the applied wave length. For any electrode length less than one wave length or for an electrode length intermediate between the successive whole multiples of the applied wave length some energy will be propagated in the direction towards the impedance 21. The ratio of the energy so propagated to that propagated towards the output becomes increasingly small as the electrode length is increased. This is because the vectors add algebraically in the same phase relation "for propagation in the direction of the output, thereby producing a total energy which increases with electrode length while in the reverse direction the vectors cannot combine algebraically to a value greater than would be the case'if the electrodes wereone-half wave length long. That an electrode length equal .to one-half wave length will produce the greatest transfer of energy towards the impedance 21 will betapparent when it is considered that up to one-half wave length all of the vectors will add together in the same linear direction regardless of their angular displacement while vectors beyond one-half wave length all add up in the opposite linear .direction regardless of their angular displacement and hence oppose the .vectors of the first half-wave.

As the incoming wave from the left travels along with its radiallines of force extending between the filament-cathode I3 and the grid I 5, its energy will gradually be absorbed in the reaction which it encounters by which the anode current is varied to'give an amplified reproduction. Whatever energy the incoming wave may retain when it reaches the right-hand end of the tube will be impressed upon the bridge consisting of the condenser sistance 21'. These are designed to aiford a proper impedance termination so that such residual input wave energy will be absorbed and not reflected.

Fig. 5 is a highly diagrammatic representation of Fig. l, the identification of the corresponding parts being made apparent by the use of the same reference numerals. In Fig. 5 the grid and the anode are shown only at one side of the cathode instead of at both sides, as in Fig. 1. The sinusoidal line 32 on the grid line l5 as axis represents the incoming waves of electromotive force between the cathode l8 and the grid l5. At the crests of these waves in the line 32 the normal radial electron flow from the cathode l8 through the grid I5 is increased. This is indi cated by the stippling 33' under each such crest. As the wave moves on to the right, the cloud of electrons moves o't radially so that behind each wave crest there will be trailing an inclined cloud 33 of electrons, the individual electrons moving radially as indicated by the arrow 34 but the region of increased density, that is the cloud 33, moving to the right, as indicated by the arrow 35.

In the apparatusof Figs. 1 and 5 the motion of the individual electrons is not purely oscillatory, There is a continuous radial drift of electrons imposed by the plate battery 24. This con- I5'26' and the reamasaa tinuous radial motion consists of a steady intensity determined by the plate battery and a superposed oscillatory intensity determined by the incoming waves. The resultant is a fluctuating intensity. Although the radial drift of the electrons occurs no farther to the right than the glass seal it, its fluctuations to that point produce electromagnetic waves which are continued to the right between the conductors 30 and ii and thence between the conductors l2 and II.

The tube may be operated in a somewhat different manner, as indicated in Fig. 6. Whereas in Figs. 1 and 5 the grid is moderately negative and the anode is strongly positive, in Fig. 8 the grid is made strongly positive and the anode moderately negative. At the input end on the left the inner and outergconcentric conductors are connected to the cathode it at 20 and to the anode l3 at II", respectively and an impedance bridge of capacity I5"26' and resistance 21" is placed across the left end of the cathode l8 and grid l5. At the right efid the grid I! is con-' nected to the outer concentric conductor II' and the cathode I8 is connected through a condenser l6"-i9" to the inner conductor l2. An impedance of capacity l3'26" and resistance 21' is bridged across the cathode i8 and anode l3 at the right. With no input waves applied at the left end of the amplifier to affect the normal potential of the anode l3 and the filament l8, many electron paths will be as indicated by the arrow 36; that is, electrons emitted by the cathode i8 will be accelerated by the positive grid I5 and will pass through the grid openings into the grid-anode space. The energy acquired by these electrons during acceleration will cause them to travel a considerable distance in the grid-anode space, against the attraction of the positive grid I5 and the repulsion of the negative anode l3, before coming to rest and starting back toward the grid. By suitably adjusting the grid and anode potentials this turning point of the electrons can be brought very close to the anode. The cloud of momentarily stationary electrons thus formed becomes a virtual cathode from which electrons may be readily drawn to the anode. Owing to the close proximity of anode and virtual cathode, a comparatively small increase of anode potential in the positive direction will draw a relatively large number of electrons from the virtual cathode.

With no input to the amplifier, all the electrons emitted by the cathode eventually reach the grid, assuming that the grid is sufllciently positive to prevent the formation of space charge in the grid-cathode region. Thus for no input there is a constant flow of electrons from cathode to grid. When an input wave is applied at the left between anode and cathode, many electrons are drawn from the virtual cathode to the anode, the number of these electrons fluctuating in accordance with the variations of the anode potential. Consequently the number of electrons remaining, which are drawn to the grid, also fluctuates in accordance with the anode potential variations, the number reaching the grid decreasing as the anode potential increases in the positive direction. The result of this action is an amplified wave between grid and cathode, which, as it is propagated along the length of the electrodes, undergoes the same building-up as described in the negative grid amplifier of Fig. 5.

Figs. 1 and 5 show a directly heated cathode. For an indirectly heated cathode suitable modification is indicated in Fig. 'l, as will readily be apparent.

As has been mentioned heretofore, a short section of the elongated vacuum tube described herein may, in eifect, be considered as equivalent to a conventional three-element vacuum tube. Additional grids or elements for shielding or other purpom recognized in conventional vacuum tube practice may be employed in this elongated type of tube. 4

I claim:

1. Apparatus for amplifying the energy of a high frequency wave train comprising a vacuum tube having cathode, anode and control electrodes lying in the direction of propagation and each having a length several times that of the wave length of said frequency so that the wave propagated in one direction is greater than that in the reverse direction, an input connection to apply said wave train to certain of said electrodes at one end of the tube for propagation along said electrodes, and an output connection to at least one different electrode at the other end of the tube to take of! a wave propagated along said different electrode.

2. Apparatus for amplifying the energy of a train of high frequency waves comprising a plurality of electrodes paralleling each other over a distance of more than one wave length of said frequency in the direction of propagation so that the wave propagated in one direction is greater than that in the reverse direction, means to impress the wave configuration on one pair of said electrodes for propagation along said electrodes, output connections to a different pair of said electrodes, and operating potentials so, applied to said electrodes as to produce on said different pair of said electrodes an amplified copy of the wave configuration applied to said first pair.

3. In combination, a pair of conductors for the transmission of high frequency waves, a vacuum tube having more than two electrodes at least two of which extend over a distance of more thanone wave length of said frequency substantially in the same direction and respectively in continuation of said pair of conductors so that the wave propagated in one direction is greater than that in the reverse direction, and another pair of conductors similar to said first mentioned pair extending on in substantially the same direction from a different pair of electrodes of said vacuum tube.

4. A vacuum tube amplifier for high frequency waves having a plurality of electrodes extending parallel to each other over a distance of more than one wave length of said frequency in one and the same direction so that the .wave propagated in one direction is greater than that in the reverse direction, means to apply an input high frequency electromotive force to a pair of said electrodes at one end of said tube so that said electromotive force may be propagated along the length of said electrodes, and operating voltages applied to certain of said electrodes so as to gradually build up in response to said propagation a corresponding amplified output electromotive force propagated along another pair of electrodes toward and to the other end of the tube.

5. In combination, a long vacuum tube having electrodes extending along the length of the tube a distance of more than one wave length of an applied wave so that the wave propagated in one direction is greater than that in the reverse direction, input conductors connected at one end to two of these electrodes and output conductors connected at the other end to a difierent pair of these electrodes.

f 6. In combination, a pair of conductors for the transmission of high frequency waves, a vacuum tube having a plurality oi electrodes, two of these extending substantially parallel with each other in the same direction and respectively in continuation of said two conductors, at least one other electrode substantially parallel with said two electrodes, said electrodes extending for a distance of more than one wave length oi. the'applied wave so that the wave propagated in one direction is greaterthan that in the reverse direction, and two more conductors simiiar to the first pair extending on in substantially the same direction and respectively in'continuation of a pair of said electrodes, this pair having at least one member difierent from the members of the first mentioned pair.

7. In combination, a vacuum tube including a pair of input electrodes and including a pair of output electrodes, said electrodes extending coaxially a distance of more than one wave length oi an applied wave in the direction of wave propagation so that the wave propagated in one directionis greater than that in the reverse direction, a concentric conductor pair coaxial with the tube and connected at one end of the tube to said input coaxial electrodes, and a like conductor pair also coaxial with the tube and cennected at the other end of the tube to said output coaxial electrodes so that transmission may take place through the tube from one concentric conductor pair to the other.

8. In combination, a long vacuum tube having three electrodes in which the rate of electron emission to the anode varies sinusoidally ever the length of said anode and the phase of this sinusoidal variation changes progressively in one direction along the anode, a concentric conductor system extending in the same direction and having its two conductors connected respectively at one end of said tube to two of its electrodes, a

similar concentric conductor system extending in the same direction at the other ,end of the tube and having its two conductors connectedat that end to two electrodes of the tube, the connections at one end being tapered with the proper ratio of radii so as to bring the concentric conductor system to the same dimensions on both the input and the output ends of the tube.

9. In combination, a concentric conductor system, a three-electrode vacuum tube interposed therein having its electrodes extending through the tube a distance of more than one wave length of an applied wave and disposed symmetrically around a common axis with the concentric conductor system so that ,the wave propagated in one direction is greater than that in the reverse direction, certain of said electrodes and certain of the conductors of said concentric conductor system having terminating portions lying adjacent each other to form capacity connections between certain tube electrodes and certain conductors of said concentric conductor system.

10. A cylindrical vacuum tube with axial oath= ode, coaxial outer cylindrical anode, and coaxial intermediate cylindrical grid, said electrodes extending through said tube a distance of more than one wave length of an applied wave so that the wave propagated in one direction is greater than that in the reverse direction, a pair of input conductors connected to the cathode and grid at one end, a pair of output conductors connected to the anode and one of the other electrodes at the other amazes end, one oi the input conductors having a flange adjacent a corresponding flange on one 01 said electrodes to constitute closely spaced condenser plates on respective sides or a gap, thus forming a capacitative connection, and anoutput conductor similarly capacitatively connected to another electrode.

11. In combination, a long vacuum tube having a plurality of electrodes extending through the. tube a distance of more than one wave length of an applied wave and disposed symmetrically around a common axis so that the wave propagated in one direction isgreater than that in the reverse direction, input conductors connected tocertain of said electrodes at one end, output con ductors connected to a diflerent pair of eiectrodes at the opposite end, and an impedance matching termination bridged across two electrodes of the tube at one end thereof.

12. A cylindrical vacuum tube with axial cathode, coaxial outer cylindrical anode, and coaxial intermediate cylindrical grid, said electrode extending through the tube over a distance of more than one wave length 0! the applied wave so that the wave propagated in one direction is greater than that in the reverse direction, a pair of input conductors connected to the cathode and another electrode at one end, a pair of eutput conductors connected to the cathede and yet another electrode at the other end, an annular condenser and a resistance in series bridged across between an electrode connected to an input conductor and an unconnected electrode at the input end 0! the tube, and a like bridging combination across between a different pair of electrodes at the output end. 13. The method of amplifying high frequency waves which consists in propagating a wave from point to point for a distance of more than a wave length along 'a-conductive ath in an evacuated space, prodiicing at each point by the electrcmotive force of the wave thus propagated along the path a corresponding change in each element of the field along the corresponding length of another path in said evacuated space, and in said latter path efi'ectirely adding to each other elements of the wave propagated in the uated space, producing at each point by the electromotive force of the wave thus propagated along the path a corresponding change in each element of the field along the corresponding length of another path in said evacuated space, and in said latter path effectively adding to each other elements of the wave propagated in the direction of transmission while eflectively balancing out elements of the wave propagated in the reverse direction.

15. The method of amplification of a. wave train which consists in cumulatively amplifying the energy of the wave train at successive points distributed continuously along a conductive path in an evacuated space extending over several wave lengths oLthe wave train.

16. The method of amplification of a wave train which consists in cumulatively amplifying ,the energy of the wave train at successive points distributed continuously along a conductive path in an evacuated space extending in the direction of propagation over a distance of as much as one wave length.

1'7. The method of amplifying high frequency electric waves which consists in propagating a wave along a path formed in an evacuated space between a cathode and a parallel control electrode extending over a distance of at least a wave length, varying the rate of electron flow from the extended cathode element over the cathode length in accordance with the instantaneous distribution of force in the electric waves traveling in the direction in which said cathode extends and in the region between said cathode and the parallel control electrode, producing corresponding changes in the field along a third electrode which add cumulatively in the direction of transmission, and taking off the amplified energy which is thereby determined in the region between said third electrode and another electrode.

18. The method of amplifying high frequency waves which consists in propagating a wave along a conductive path in an evacuated space for a distance of at least a wave length, amplifying each element of said wave at each of a number of successive points along the length of said path in the direction of propagation, and

cumulating the resultant amplified components propagated along the length of the path in that same direction.

19. The method of amplifying high frequency waves between a pair of conductors which consists in propagating a wave along said conductors in an evacuated space for a distance of at least a wave length so that the wave component propagated in one direction is greater than the component in the reverse direction, emittin electrons within said space along the length of one conductor with the electron paths transverse thereto, controlling the electron discharge current at each point along said conductor within said space in accordance with the incoming wave of electromotive force propagated along the pair of conductors within the space, thereby producing a corresponding amplified wave.

20. The method of amplifying high frequency waves between a pair of conductors which consists in propagating a wave along said conductors in an evacuated space for a distance of at least a wave length so that the wave component propagated in one direction is greater than the component in the reverse direction, emitting electrons along the length of one of said conductors within said space, varying the discharge density of said electrons at each point along said pair of conductors within said space in accordance with the impressed wave, thereby producing an amplified electron discharge current from point to point along the emitting conductor, and taking this current off on a pair of conductors in sabstantial alignment with the first pair.

RALPH K. POTTER. 

